booklet vs blue book

booklet and blue book both are nouns.

Word	Noun	Adjective	Verb	Adverb
booklet	Yes	No	No	No
blue book	Yes	No	No	No

As nouns, blue book is a hyponym of booklet; that is, blue book is a word with a more specific, narrower meaning than booklet:

Other hyponyms of booklet include ticket book.

booklet (noun)	blue book (noun)
a small book usually having a paper cover	a register of persons who are socially prominent
	a report published by the British government; bound in blue
	a blue booklet used in universities for writing examinations